R Coding Workshop: 4th Meeting

GIS & Geospatial Data Analysis (Fall 2025)

R Coding Workshop: 4th Meeting

Outline

• R Functions
• dplyr functions
  • arrange()
  • slice_sample()
• define your own function
• ggplot2

R Functions

library(tidyverse)

── Attaching core tidyverse packages ──────────────────────── tidyverse 2.0.0 ──
✔ dplyr     1.1.4     ✔ readr     2.1.5
✔ forcats   1.0.0     ✔ stringr   1.5.1
✔ ggplot2   3.5.1     ✔ tibble    3.3.0
✔ lubridate 1.9.3     ✔ tidyr     1.3.1
✔ purrr     1.0.2     
── Conflicts ────────────────────────────────────────── tidyverse_conflicts() ──
✖ dplyr::filter() masks stats::filter()
✖ dplyr::lag()    masks stats::lag()
ℹ Use the conflicted package (<http://conflicted.r-lib.org/>) to force all conflicts to become errors

library(sf)

Linking to GEOS 3.13.0, GDAL 3.8.5, PROJ 9.5.1; sf_use_s2() is TRUE

library(mapview)
library(rnaturalearth)
library(viridis)

Le chargement a nécessité le package : viridisLite

Using base and imported functions

Functions from Base R

class(print) |> print()

[1] "function"

class(class)

[1] "function"

long_df <- tibble(
    value = 1:37
)
print(long_df)

# A tibble: 37 × 1
   value
   <int>
 1     1
 2     2
 3     3
 4     4
 5     5
 6     6
 7     7
 8     8
 9     9
10    10
# ℹ 27 more rows

long_df |> print(n = 37)

# A tibble: 37 × 1
   value
   <int>
 1     1
 2     2
 3     3
 4     4
 5     5
 6     6
 7     7
 8     8
 9     9
10    10
11    11
12    12
13    13
14    14
15    15
16    16
17    17
18    18
19    19
20    20
21    21
22    22
23    23
24    24
25    25
26    26
27    27
28    28
29    29
30    30
31    31
32    32
33    33
34    34
35    35
36    36
37    37

Imported functions

class(select)

[1] "function"

class(mapview)

[1] "standardGeneric"
attr(,"package")
[1] "methods"

Components of a Function

When we want to write our own Function

• copy-and-paste
• vector operations
• creating plots

Components of a Function

• Function Name: Usually a verb
• Parameters: Variable provided when you defined your function,they act as a placeholder for expected input
• Arguments: Variable specified at the time you use the function
• Return: Output of the function

add_four <- function(x) x + 4
add_four |> class() |> print()

[1] "function"

add_four <- function(x) x + 4
add_four |> class() |> print()

[1] "function"

a <- 1.46
add_four(a)

[1] 5.46

v1 <- c(1, 9, 8, 8)
add_four(v1)

[1]  5 13 12 12

v1 + 4

[1]  5 13 12 12

sapply(v1, add_four)

[1]  5 13 12 12

long_df$value |> add_four()

 [1]  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
[26] 30 31 32 33 34 35 36 37 38 39 40 41

book_challenge_sf <- st_read('data/book-challenges-state-sf.gpkg')

Reading layer `book-challenges-state-sf' from data source 
  `/Users/toyuan/dohnanyi/data/book-challenges-state-sf.gpkg' 
  using driver `GPKG'
Simple feature collection with 51 features and 9 fields
Geometry type: MULTIPOLYGON
Dimension:     XY
Bounding box:  xmin: -179.1435 ymin: 18.90612 xmax: 179.7809 ymax: 71.4125
Geodetic CRS:  WGS 84

book_challenge_sf |> mapview(zcol = 'count')

Getting familiar with how functions work

• paste() and paste0() function

create_label <- function(unit, count) {
    paste0(unit, ': ', count)
}

book_challenge_sf <- book_challenge_sf |> mutate(lab = create_label(gn_name, count))
book_challenge_sf |> mapview(zcol = 'count', label = 'lab')

Plotting Function

book_challenge_sf |>
  filter(!(postal %in% c('HI', 'AK'))) |>
  ggplot() +
  geom_sf(
    aes(fill = count),
    color = 'white',
    size = 0.1
  ) +
  geom_sf_label(
    aes(label = postal),
    size = 2.5,
    fill = 'white',
    alpha = 0.7,
    color = 'black'
  ) +
  scale_fill_viridis(na.value = '#E2E2E2') +
  theme_minimal() +
  labs(
    title = 'Book Challenges by State',
    subtitle = '2000-2010'
  )

Warning in st_point_on_surface.sfc(sf::st_zm(x)): st_point_on_surface may not
give correct results for longitude/latitude data

plot_state_choropleth <- function(sf, col_str, plt_title) {
    sf |>
    filter(!(postal %in% c('HI', 'AK'))) |>
    ggplot() +
    geom_sf(
      aes_string(fill = col_str),
      color = 'white',
      size = 0.1
    ) +
    geom_sf_label(
      aes(label = postal),
      size = 2.5,
      fill = 'white',
      alpha = 0.7,
      color = 'black'
    ) +
    scale_fill_viridis(na.value = '#E2E2E2') +
    theme_minimal() +
    labs(
      title = plt_title,
      subtitle = '2000-2010'
    )
}

plot_state_choropleth(
    book_challenge_sf,
    'count',
    'Book Challenges by State'
    )

Warning: `aes_string()` was deprecated in ggplot2 3.0.0.
ℹ Please use tidy evaluation idioms with `aes()`.
ℹ See also `vignette("ggplot2-in-packages")` for more information.

Warning in st_point_on_surface.sfc(sf::st_zm(x)): st_point_on_surface may not
give correct results for longitude/latitude data

plot_state_choropleth(book_challenge_sf, 'median_income', 'State Median Income')

Warning in st_point_on_surface.sfc(sf::st_zm(x)): st_point_on_surface may not
give correct results for longitude/latitude data

book_challenge_sf |> plot_state_choropleth('political_value_index', 'Political Value Index')

Warning in st_point_on_surface.sfc(sf::st_zm(x)): st_point_on_surface may not
give correct results for longitude/latitude data

arrange()

• Sort observations by column value

book_challenge_sf |>
  arrange(desc(count)) |>
  pull(lab)

 [1] "Pennsylvania: 147"        "Oregon: 118"             
 [3] "Colorado: 80"             "California: 50"          
 [5] "Illinois: 39"             "Michigan: 34"            
 [7] "Virginia: 33"             "Ohio: 29"                
 [9] "Florida: 26"              "New York: 24"            
[11] "Oklahoma: 23"             "North Carolina: 20"      
[13] "Indiana: 20"              "Minnesota: 17"           
[15] "South Carolina: 15"       "Idaho: 14"               
[17] "Vermont: 13"              "Georgia: 13"             
[19] "Kansas: 13"               "Iowa: 13"                
[21] "Kentucky: 13"             "Tennessee: 13"           
[23] "Arizona: 12"              "Louisiana: 12"           
[25] "New Jersey: 11"           "Missouri: 11"            
[27] "Alabama: 10"              "Wisconsin: 10"           
[29] "Washington: 9"            "Alaska: 9"               
[31] "Massachusetts: 8"         "Montana: 7"              
[33] "New Hampshire: 7"         "North Dakota: 6"         
[35] "Connecticut: 6"           "Maryland: 5"             
[37] "Arkansas: 5"              "Wyoming: 4"              
[39] "Maine: 3"                 "New Mexico: 3"           
[41] "Rhode Island: 3"          "South Dakota: 3"         
[43] "West Virginia: 3"         "Delaware: 2"             
[45] "Nebraska: 2"              "Mississippi: 1"          
[47] "Utah: 1"                  "Texas: NA"               
[49] "District of Columbia: NA" "Hawaii: NA"              
[51] "Nevada: NA"              

book_challenge_sf |>
  arrange(political_value_index) |>
  select(gn_name, count, political_value_index)

gn_name	count	political_value_index	geom
Utah	1	-20.2	MULTIPOLYGON (((-111.0502 4…
Wyoming	4	-19.7	MULTIPOLYGON (((-109.0463 4…
Idaho	14	-17.4	MULTIPOLYGON (((-117.0382 4…
Oklahoma	23	-16.9	MULTIPOLYGON (((-103.0002 3…
Nebraska	2	-13.5	MULTIPOLYGON (((-104.0537 4…
Alaska	9	-13.4	MULTIPOLYGON (((-141.0056 6…
Alabama	10	-13.2	MULTIPOLYGON (((-87.41958 3…
Kansas	13	-11.5	MULTIPOLYGON (((-102.0396 3…
North Dakota	6	-10.4	MULTIPOLYGON (((-104.0476 4…
Kentucky	13	-10.4	MULTIPOLYGON (((-89.42446 3…
Louisiana	12	-9.7	MULTIPOLYGON (((-89.52599 3…
Mississippi	1	-9.5	MULTIPOLYGON (((-88.40221 3…
South Dakota	3	-8.9	MULTIPOLYGON (((-104.0567 4…
Arkansas	5	-8.8	MULTIPOLYGON (((-90.30422 3…
Tennessee	13	-8.7	MULTIPOLYGON (((-90.30422 3…
West Virginia	3	-7.9	MULTIPOLYGON (((-82.58945 3…
South Carolina	15	-7.8	MULTIPOLYGON (((-78.57316 3…
Montana	7	-7.1	MULTIPOLYGON (((-116.0482 4…
Georgia	13	-6.8	MULTIPOLYGON (((-80.89029 3…
Indiana	20	-6.2	MULTIPOLYGON (((-84.80608 4…
Arizona	12	-6.1	MULTIPOLYGON (((-111.0063 3…
North Carolina	20	-4.3	MULTIPOLYGON (((-76.03173 3…
Missouri	11	-3.1	MULTIPOLYGON (((-95.31725 4…
Florida	26	-1.8	MULTIPOLYGON (((-87.44734 3…
Virginia	33	-1.7	MULTIPOLYGON (((-76.01325 3…
Ohio	29	-0.7	MULTIPOLYGON (((-80.52023 4…
Colorado	80	-0.2	MULTIPOLYGON (((-109.0463 4…
Iowa	13	1.0	MULTIPOLYGON (((-96.48266 4…
New Hampshire	7	1.6	MULTIPOLYGON (((-71.50585 4…
Pennsylvania	147	2.0	MULTIPOLYGON (((-79.76301 4…
Minnesota	17	2.3	MULTIPOLYGON (((-97.22609 4…
New Mexico	3	2.4	MULTIPOLYGON (((-108.1375 3…
Wisconsin	10	2.4	MULTIPOLYGON (((-87.80425 4…
Michigan	34	3.8	MULTIPOLYGON (((-84.4913 46…
Oregon	118	4.0	MULTIPOLYGON (((-124.4924 4…
New Jersey	11	4.4	MULTIPOLYGON (((-75.54133 3…
Washington	9	5.0	MULTIPOLYGON (((-122.753 48…
Maine	3	5.5	MULTIPOLYGON (((-71.08495 4…
Delaware	2	7.0	MULTIPOLYGON (((-75.05809 3…
Connecticut	6	7.1	MULTIPOLYGON (((-73.6417 41…
California	50	7.4	MULTIPOLYGON (((-114.7243 3…
Illinois	39	7.7	MULTIPOLYGON (((-89.1237 36…
Maryland	5	8.5	MULTIPOLYGON (((-75.64786 3…
New York	24	10.2	MULTIPOLYGON (((-79.06523 4…
Rhode Island	3	11.2	MULTIPOLYGON (((-71.23686 4…
Massachusetts	8	11.7	MULTIPOLYGON (((-71.19396 4…
Vermont	13	13.4	MULTIPOLYGON (((-73.35134 4…
Texas	NA	NA	MULTIPOLYGON (((-103.3115 2…
District of Columbia	NA	NA	MULTIPOLYGON (((-77.02293 3…
Hawaii	NA	NA	MULTIPOLYGON (((-154.8996 1…
Nevada	NA	NA	MULTIPOLYGON (((-114.0425 4…

book_challenge_df <- read_csv('data/book-challenge11.csv')

Rows: 931 Columns: 17
── Column specification ────────────────────────────────────────────────────────
Delimiter: ","
chr   (3): title, author, state
dbl  (13): book_id, year, removed, explicit, antifamily, occult, language, l...
date  (1): date

ℹ Use `spec()` to retrieve the full column specification for this data.
ℹ Specify the column types or set `show_col_types = FALSE` to quiet this message.

book_challenge_df |> arrange(author, title) |> head(10)

title	book_id	author	date	year	removed	explicit	antifamily	occult	language	lgbtq	violent	state	political_value_index	median_income	hs_grad_rate	college_grad_rate
Go and Come Back	721	Abelove, Joan	2000-06-18	2000	0	1	0	0	0	0	0	WV	-7.9	-7290.0	-4.361958	-9.2237299
Finding Our Way–The Teen Girl Survival Guide	695	Abner, Allison	2002-05-21	2002	0	1	0	0	0	0	0	AZ	-6.1	3490.5	1.438042	-0.5237299
Death Blossoms	522	Abu-Jamal, Mumia	2005-07-03	2005	0	0	0	0	0	0	0	OR	4.0	1274.5	5.538042	1.0762701
Tijuana Bibles	1811	Adelman, Bob	2000-06-29	2000	0	1	0	0	0	0	1	OR	4.0	1274.5	5.538042	1.0762701
Art for Lovers	160	Adler, Sabine	2005-04-08	2005	0	0	0	0	0	0	0	OR	4.0	1274.5	5.538042	1.0762701
Psychic Academy Series	1484	Aki, Katsu	2008-06-07	2008	0	0	0	0	0	0	0	VA	-1.7	11296.0	1.938042	5.4762701
Monkey High Vol. 3	1277	Akira, Shouko	2009-05-06	2009	0	0	0	0	0	0	0	MI	3.8	2966.0	3.838042	-2.2237299
Absolutely True Diary of a Part-Time Indian, The	69	Alexie, Sherman	2008-10-02	2008	1	0	0	0	0	0	0	IA	1.0	3921.5	6.538042	-2.8237299
Absolutely True Diary of a Part-Time Indian, The	69	Alexie, Sherman	2009-05-04	2009	0	1	0	0	1	0	0	IL	7.7	6489.5	1.838042	2.0762701
Absolutely True Diary of a Part-Time Indian, The	69	Alexie, Sherman	2010-05-12	2010	1	0	0	0	1	0	1	MO	-3.1	1279.5	1.738042	-2.4237299

slice_sample()

book_challenge_df |> slice_sample(n = 10)

title	book_id	author	date	year	removed	explicit	antifamily	occult	language	lgbtq	violent	state	political_value_index	median_income	hs_grad_rate	college_grad_rate
Summer of My German Soldier	1739	Greene, Bette	2002-04-08	2002	0	0	0	0	1	0	0	AR	-8.8	-6258.5	-4.2619579	-7.32373
Between a Rock and a Hard Place	223	Carter, Alden	2000-06-29	2000	0	0	0	0	1	0	0	OR	4.0	1274.5	5.5380421	1.07627
Whale Talk	1941	Crutcher, Chris	2007-10-25	2007	1	0	0	0	1	0	0	OH	-0.7	2469.0	3.4380421	-2.92373
Harry Potter and the Chamber of Secrets	868	Rowling, J.K.	2000-03-01	2000	1	0	0	1	0	0	0	MI	3.8	2966.0	3.8380421	-2.22373
Boy Gets Girl: A Play	295	Gilman, Rebecca	2005-08-26	2005	1	0	0	0	1	0	0	NY	10.2	5007.5	-0.4619579	3.37627
Adventures of Huckleberry Finn, The	75	Twain, Mark	2007-08-02	2007	0	0	0	0	0	0	0	MN	2.3	15378.0	8.3380421	3.37627
We All Fall Down	1930	Cormier, Robert	2004-01-12	2004	1	0	0	0	1	0	1	KS	-11.5	144.5	6.4380421	1.77627
I Am Charlotte Simmons	950	Wolfe, Tom	2006-07-28	2006	0	1	0	0	1	0	0	MO	-3.1	1279.5	1.7380421	-2.42373
Adventures of Tom Sawyer, The	78	Twain, Mark	2007-08-02	2007	0	0	0	0	1	0	0	IA	1.0	3921.5	6.5380421	-2.82373
Tamar	1755	Chamberlain, Ann	2002-09-17	2002	0	0	0	0	0	0	0	OR	4.0	1274.5	5.5380421	1.07627

book_challenge_df |>
  filter(state == 'PA') |>
  slice_sample(n = 10)

title	book_id	author	date	year	removed	explicit	antifamily	occult	language	lgbtq	violent	state	political_value_index	median_income	hs_grad_rate	college_grad_rate
Mythology	1012	NA	2001-04-25	2001	0	0	0	0	0	0	0	PA	2	4218	2.338042	-1.62373
Breath	312	Winton, Tim	2009-11-09	2009	0	0	0	0	0	0	0	PA	2	4218	2.338042	-1.62373
Starplace, The	1699	Grove, Vicki	2009-11-09	2009	0	0	0	0	0	0	0	PA	2	4218	2.338042	-1.62373
Beyond the Chocolate War	228	Cormier, Robert	2009-11-09	2009	0	0	0	0	0	0	0	PA	2	4218	2.338042	-1.62373
Love & Sex	1183	Cart, Michael	2009-11-09	2009	0	0	0	0	0	0	0	PA	2	4218	2.338042	-1.62373
God Box, The	724	Sanchez, Alex	2009-11-09	2009	0	0	0	0	0	0	0	PA	2	4218	2.338042	-1.62373
As I Lay Dying	165	Faulkner, William	2009-11-09	2009	0	0	0	0	0	0	0	PA	2	4218	2.338042	-1.62373
Braless in Wonderland	307	Fischer, Debbie Reed	2009-11-09	2009	0	0	0	0	0	0	0	PA	2	4218	2.338042	-1.62373
Keeping You A Secret	1069	Peters, Julie Anne	2009-11-09	2009	0	0	0	0	0	0	0	PA	2	4218	2.338042	-1.62373
Like Sisters on the Homefront	1139	Williams-Garcia, Rita	2000-08-28	2000	1	0	0	0	0	0	0	PA	2	4218	2.338042	-1.62373